1. Field of the Invention
The present invention relates to a pH dependent ion exchange material which can selectively bind to a nucleic acid, a solid substrate having the material immobilized on its surface, and a method of isolating a nucleic acid using the material or the solid substrate.
2. Description of the Related Art
Methods of isolating nucleic acids using pH dependent ion exchange matrices are known. For example, U.S. published patent application No. 2001/0018513 describes a method of isolating a nucleic acid using a material containing an ionisable group which is positively charged at a first pH such that it can be bound to the nucleic acid and releasing the nucleic acid at a second pH which is higher than the first pH. Examples of the material containing an ionisable group include N-2-acetamido-2-aminoethanesulfonic acid (ACES), N-2-acetamido-2-imidodiacetic acid (ADA), N-trihydroxymethyl-methyl-2-aminoethanesulfonic acid (TES) and trihydroxymethylaminoethane (Tris), etc. U.S. Pat. No. 6,310,199 describes a method of isolating a nucleic acid using a pH dependent ion exchange matrix comprising a silica magnetic particle and a plurality of first ion exchange ligands, each first ion exchange ligand comprising an aromatic hydrocarbon ring, a spacer covalently attached to the aromatic hydrocarbon ring, and a linker comprising a linker alkyl chain attached to the silica magnetic particle at its first end and attached to the spacer at its second end.
However, there is still a need for materials containing an ionisable group which can bind to the nucleic acids at a high speed and have a high efficiency of releasing the nucleic acids when pH is increased. In addition, the conventional materials bind not only to DNAs but also to proteins and have low selectivity to nucleic acids. Thus, the inventors of the present invention searched for materials which can bind the nucleic acids with high selectivity and have a remarkably high efficiency of releasing the nucleic acids when pH is increased, and discovered a pH dependent ion exchange material containing both an acid functional group having a pKa value of 4 or less and a base.